Electrochemical cells for harvesting and storing energy and devices including the same

ABSTRACT

Electrochemical cells that include composite gel positioned between the first electrode and second electrode, where the composite gel comprises an electrolyte, a polyaryl amine, and an oxidant. The utilized composite gels are easy to produce at a low-cost, which makes them suitable in a number of different applications electrochromic devices, supercapacitors, solar cells, and hybrid photoactive supercapacitors.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation from the U.S. patent application Ser.No. 17/189,625, which claims the benefit of and priority from the U.S.Provisional Patent Application No. 62/986,874, filed on Mar. 9, 2020.The disclosure of each of the above-identified patent applications isincorporated by reference herein.

RELATED ART

To endure the evolution of green energy sources, harvesting, storage,and delivering energy is paramount to limit the dependence onnonrenewable sources. Electrochemical devices are exemplary applicationsto achieve this demand and cope with the intermittent nature ofrenewable energy sources. Some examples of such devices aresupercapacitors, dye sensitized solar cells (DSSCs), and electrochromicwindows. However, there is a need for solar cells and other relateddevices to have the ability to store energy within the device.

SUMMARY OF THE INVENTION

In accordance with the purpose(s) of the present disclosure, as embodiedand broadly described herein are electrochemical cells that includecomposite gel positioned between the first electrode and secondelectrode, wherein the composite gel comprises an electrolyte, apolyaryl amine, and oxidant. The composite gels described herein areeasy to produce at a low-cost, which makes them suitable in a number ofdifferent applications electrochromic devices, supercapacitors, solarcells, and hybrid photoactive supercapacitors.

Other systems, methods, features, and advantages of the presentdisclosure will be or become apparent to one with skill in the art uponexamination of the following drawings and detailed description. It isintended that all such additional systems, methods, features, andadvantages be included within this description, be within the scope ofthe present disclosure, and be protected by the accompanying claims. Inaddition, all optional and preferred features and modifications of thedescribed embodiments are usable in all aspects of the disclosure taughtherein. Furthermore, the individual features of the dependent claims, aswell as all optional and preferred features and modifications of thedescribed embodiments are combinable and interchangeable with oneanother.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the present disclosure can be better understood withreference to the following drawings. The components in the drawings arenot necessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the present disclosure. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIGS. 1A, 1B, 1C, 1D, 1E, and 1F show (a) a UV-vis absorption spectrum,(b) FTIR spectrum, and (c) Raman spectrum of the composite gel ofPVA-HCI-APS-PANI, PVA, PVA-HC, and PVAHCI-APS. (d) CV result and (e)Nyquist plot from the EIS study of a thin composite gel layer sandwichedbetween two glassy carbon electrodes and (f) equivalent electricalcircuit model of the complex impedance in the gel. The inset figure inplot (d) shows the transition of PANI from ES to LS form.

FIGS. 2A, 2B, and 2C show (a) a schematic diagram; (b) a picture of thefabricated supercapacitor with CNT based porous electrodes and a thinlayer of the composite gel as the electrolyte and active redox material;and (c) CV results from devices with two different gels: PVA-HCI andPVA-HCI-APS-PANI.

FIGS. 3A, 3B, and 3C show (a) a schematic diagram; (b) a picture of thefabricated electrochemical cell with the composite gel; and (c) J-Vcharacteristics of the electrochemical cell device in dark and light.

FIGS. 4A, 4B, 4C, 4D, and 4E show (a) a schematic diagram; (b) a pictureof the hybrid photoactive supercapacitor for energy harvesting andstorage; (c) CV of the hybrid device; (d) open circuit voltage; and (e)short circuit current versus time under light and dark pulses.

FIGS. 5A, 5B, 5C, 5D, 5E, and 5F show (a) a schematic diagram; (b)pictures of the fabricated electrochromic device at three differentmodes; (c) CV result showing the redox peaks; (d) electric currentthrough the device in response to (e) the applied voltage pulses; and(f) transmittance of the device in two different biasing conditions.

FIGS. 6A, 6B, 6C, and 6D show the steps of fabricating the PANIcomposite gel: (a) the gelling process of PVA in HCI and theinteractions with APS and PANI; (b) chemical reactions in threedifferent oxidation states of PANI; (c) energy level diagram in theelectrochemical cell and the hybrid photoactive supercapacitor forenergy harvesting. The energy levels are versus the vacuum level. Toexplain the process, the interaction between PANI and the ionic chargesare shown as two different layers; however, that interaction occurs inthe bulk gel electrolyte. (d) Loss of electron in emeraldine andconversion to pernigraniline with stored energy in the polymer.

FIGS. 7A and 7B depict electrochemical cells described herein.

Additional advantages of the invention will be set forth in part in thedescription which follows, and in part will be obvious from thedescription, or can be learned by practice of the invention. Theadvantages of the invention will be realized and attained by means ofthe elements and combinations particularly pointed out in the appendedclaims. It is to be understood that both the foregoing generaldescription and the following detailed description are exemplary andexplanatory only and are not restrictive of the invention, as claimed.

DETAILED DESCRIPTION

Many modifications and other embodiments disclosed herein will come tomind to one skilled in the art to which the disclosed compositions andmethods pertain having the benefit of the teachings presented in theforegoing descriptions and the associated drawings. Therefore, it is tobe understood that the disclosures are not to be limited to the specificembodiments disclosed and that modifications and other embodiments areintended to be included within the scope of the appended claims. Theskilled artisan will recognize many variants and adaptations of theaspects described herein. These variants and adaptations are intended tobe included in the teachings of this disclosure and to be encompassed bythe claims herein.

Although specific terms are employed herein, they are used in a genericand descriptive sense only and not for purposes of limitation.

As will be apparent to those of skill in the art upon reading thisdisclosure, each of the individual embodiments described and illustratedherein has discrete components and features which may be readilyseparated from or combined with the features of any of the other severalembodiments without departing from the scope or spirit of the presentdisclosure.

Any recited method can be carried out in the order of events recited orin any other order that is logically possible. That is, unless otherwiseexpressly stated, it is in no way intended that any method or aspect setforth herein be construed as requiring that its steps be performed in aspecific order. Accordingly, where a method claim does not specificallystate in the claims or descriptions that the steps are to be limited toa specific order, it is no way intended that an order be inferred, inany respect. This holds for any possible non-express basis forinterpretation, including matters of logic with respect to arrangementof steps or operational flow, plain meaning derived from grammaticalorganization or punctuation, or the number or type of aspects describedin the specification.

All publications mentioned herein are incorporated herein by referenceto disclose and describe the methods and/or materials in connection withwhich the publications are cited. The publications discussed herein areprovided solely for their disclosure prior to the filing date of thepresent application. Nothing herein is to be construed as an admissionthat the present invention is not entitled to antedate such publicationby virtue of prior invention. Further, the dates of publication providedherein can be different from the actual publication dates, which canrequire independent confirmation.

While aspects of the present disclosure can be described and claimed ina particular statutory class, such as the system statutory class, thisis for convenience only and one of skill in the art will understand thateach aspect of the present disclosure can be described and claimed inany statutory class.

It is also to be understood that the terminology used herein is for thepurpose of describing particular aspects only and is not intended to belimiting. Unless defined otherwise, all technical and scientific termsused herein have the same meaning as commonly understood by one ofordinary skill in the art to which the disclosed compositions andmethods belong. It will be further understood that terms, such as thosedefined in commonly used dictionaries, should be interpreted as having ameaning that is consistent with their meaning in the context of thespecification and relevant art and should not be interpreted in anidealized or overly formal sense unless expressly defined herein.

Prior to describing the various aspects of the present disclosure, thefollowing definitions are provided and should be used unless otherwiseindicated. Additional terms may be defined elsewhere in the presentdisclosure.

Definitions

As used herein, “comprising” is to be interpreted as specifying thepresence of the stated features, integers, steps, or components asreferred to, but does not preclude the presence or addition of one ormore features, integers, steps, or components, or groups thereof.Moreover, each of the terms “by”, “comprising,” “comprises”, “comprisedof,” “including,” “includes,” “included,” “involving,” “involves,”“involved,” and “such as” are used in their open, non-limiting sense andmay be used interchangeably. Further, the term “comprising” is intendedto include examples and aspects encompassed by the terms “consistingessentially of” and “consisting of.” Similarly, the term “consistingessentially of” is intended to include examples encompassed by the term“consisting of”.

As used in the specification and the appended claims, the singular forms“a,” “an” and “the” include plural referents unless the context clearlydictates otherwise. Thus, for example, reference to “a metal,” “acatalyst,” or “a product,” include, but are not limited to, combinationsor mixtures of two or more such metals, catalysts, or products, and thelike.

It should be noted that ratios, concentrations, amounts, and othernumerical data can be expressed herein in a range format. It will befurther understood that the endpoints of each of the ranges aresignificant both in relation to the other endpoint, and independently ofthe other endpoint. It is also understood that there are a number ofvalues disclosed herein, and that each value is also herein disclosed as“about” that particular value in addition to the value itself. Forexample, if the value “10” is disclosed, then “about 10” is alsodisclosed. Ranges can be expressed herein as from “about” one particularvalue, and/or to “about” another particular value. Similarly, whenvalues are expressed as approximations, by use of the antecedent“about,” it will be understood that the particular value forms a furtheraspect. For example, if the value “about 10” is disclosed, then “10” isalso disclosed.

When a range is expressed, a further aspect includes from the oneparticular value and/or to the other particular value. For example,where the stated range includes one or both of the limits, rangesexcluding either or both of those included limits are also included inthe disclosure, e.g. the phrase “x to y” includes the range from ‘x’ to‘y’ as well as the range greater than ‘x’ and less than ‘y’. The rangecan also be expressed as an upper limit, e.g. ‘about x, y, z, or less’and should be interpreted to include the specific ranges of ‘about x’,‘about y’, and ‘about z’ as well as the ranges of ‘less than x’, lessthan y′, and ‘less than z’. Likewise, the phrase ‘about x, y, z, orgreater’ should be interpreted to include the specific ranges of ‘aboutx’, ‘about y’, and ‘about z’ as well as the ranges of ‘greater than x’,greater than y′, and ‘greater than z’. In addition, the phrase “about‘x’ to ‘y’”, where ‘x’ and ‘y’ are numerical values, includes “about ‘x’to about ‘y’”.

It is to be understood that such a range format is used for convenienceand brevity, and thus, should be interpreted in a flexible manner toinclude not only the numerical values explicitly recited as the limitsof the range, but also to include all the individual numerical values orsub-ranges encompassed within that range as if each numerical value andsub-range is explicitly recited. To illustrate, a numerical range of“about 0.1% to 5%” should be interpreted to include not only theexplicitly recited values of about 0.1% to about 5%, but also includeindividual values (e.g., about 1%, about 2%, about 3%, and about 4%) andthe sub-ranges (e.g., about 0.5% to about 1.1%; about 5% to about 2.4%;about 0.5% to about 3.2%, and about 0.5% to about 4.4%, and otherpossible sub-ranges) within the indicated range.

As used herein, the terms “about,” “approximate,” “at or about,” and“substantially” mean that the amount or value in question can be theexact value or a value that provides equivalent results or effects asrecited in the claims or taught herein. That is, it is understood thatamounts, sizes, formulations, parameters, and other quantities andcharacteristics are not and need not be exact, but may be approximateand/or larger or smaller, as desired, reflecting tolerances, conversionfactors, rounding off, measurement error and the like, and other factorsknown to those of skill in the art such that equivalent results oreffects are obtained. In some circumstances, the value that providesequivalent results or effects cannot be reasonably determined. In suchcases, it is generally understood, as used herein, that “about” and “ator about” mean the nominal value indicated ±10% variation unlessotherwise indicated or inferred. In general, an amount, size,formulation, parameter or other quantity or characteristic is “about,”“approximate,” or “at or about” whether or not expressly stated to besuch. It is understood that where “about,” “approximate,” or “at orabout” is used before a quantitative value, the parameter also includesthe specific quantitative value itself, unless specifically statedotherwise.

As used herein, the terms “optional” or “optionally” means that thesubsequently described event or circumstance can or cannot occur, andthat the description includes instances where said event or circumstanceoccurs and instances where it does not.

As used herein, the term “admixing” is defined as mixing two or morecomponents together so that there is no chemical reaction or physicalinteraction. The term “admixing” also includes the chemical reaction orphysical interaction between the two or more components.

The term “alkyl group” as used herein is a branched or unbranchedsaturated hydrocarbon group of 1 to 24 carbon atoms, such as methyl,ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, pentyl, hexyl,heptyl, octyl, decyl, tetradecyl, hexadecyl, eicosyl, tetracosyl and thelike. A “lower alkyl” group is an alkyl group containing from one to sixcarbon atoms.

The term “alkenyl group” is defined herein as a C₂-C₂₀ alkyl grouppossessing at least one C═C double bond. The term “alkynyl group” isdefined herein as a C₂-C₂₀ alkyl group possessing at least one C—Ctriple bond.

The term “cycloalkyl group” as used herein is a C₃ to C₈ cyclic group.The cycloalkyl can be fully saturated or possess one or more degrees ofunsaturation. Examples of cycloalkyl groups include, but are not limitedto, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, and the like. Theterm “cycloalkyl” also includes a cycloalkyl group that has at least oneheteroatom incorporated within the ring. Examples of heteroatomsinclude, but are not limited to, nitrogen, oxygen, sulfur, andphosphorus. The cycloalkyl group can be substituted or unsubstituted.

The term “alkoxy group” as used herein is represented by —OR, where R isan alkyl group, an alkenyl group, an alkynyl group, an aryl group, acycloalkyl group, or an acyl group.

Electrochemical Cell Design

FIG. 7A schematically illustrates an example of an electrochemical celldescribed herein. Referring to FIG. 7A, electrochemical cell 10generally includes a first electrode 11 having a first surface 12 and asecond surface 13, a second electrode 14 having a first surface 15 and asecond surface 16, and a composite gel 17 positioned between the firstand second electrode. In this aspect, the composite gel 17 is in directcontact with the second surface of the first electrode and the firstsurface of the second electrode.

FIG. 7B depicts another aspect of the electrochemical cell. Theelectrochemical cell 20 has the first electrode 12 and second electrode14, where a separator 21 is positioned between the composite gel 17 andthe first electrode 12. In one aspect, the separator can be composed ofany material that prevents short-circuiting of the electrodes. In oneaspect, the separator is a non-electrically, porous conductive materialcomposed of a material such as, for example, polypropylene glass,fiberglass mesh, or Parafilm. In one aspect, the separator has athickness of about 10 μm to about 500 μm.

Depending upon the application of the electrochemical cells describedherein, the first electrode and second electrode can be composed of thesame material or different material. In one aspect, the first electrodecomprises a transparent material that permits light to pass through thematerial. In another aspect, the first and/or second electrode comprisesglass or fluorine-doped tin oxide glass. In another aspect, the firstand/or second electrode comprises porous carbon. The Examples providenonlimiting examples for producing porous carbon electrodes usefulherein.

In other aspects, the first and/or second electrode comprises glass orfluorine-doped tin oxide glass, where one surface of the first and/orsecond electrode is coated with materials such as, for example, TiO₂,ZnO, or platinum. This aspect is depicted in FIG. 3A, where TiO₂ and Ptare coated on the inner surface of each electrode (i.e., surfaces thatare in contact with the composite gel).

The composite gel can be applied to the surface of the first or secondelectrode using techniques known in the art. In one aspect, thecomposite gel can be coated on the surface of the first or secondelectrode. The thickness of the composite gel can vary depending uponthe application of the electrochemical cell. In one aspect, thecomposite gel has a thickness of from about 50 μm to about 500 μm, orabout 50 μm, about 100 μm, about 150 μm, about 200 μm, about 250 μm,about 300 μm, about 350 μm, about 400 μm, about 450 μm, or about 500 μm,where any value can be a lower and upper endpoint of a range (e.g.,about 200 μm to about 300 μm, etc.)

In certain aspects, a photosensitive dye can be applied to the surfaceof the first and/or second electrode prior to applying the composite gelon the electrode. The photosensitive dye can be applied to the surfaceof the electrode using techniques known in the art such as, for example,by chemical deposition or electrochemical deposition. Examples ofphotosensitive dyes useful herein include, but are not limited to,organic dyes, a porphine-based dyes, or a ruthenium-based dyes.

Composite Gel

The composite gel is composed of conducting polymer embedded in across-linked hydrogel with the ability of conducting both electronic andionic charges. In one aspect, the composite gel comprises anelectrolyte, a polyaryl amine, and an oxidant. Each component used toprepare the composite gels and methods for making the same are describedbelow.

In one aspect, the electrolyte as used herein is the reaction productbetween a polymer comprising a plurality of groups that can react withan acid or base. In one aspect, the electrolyte is produced by reactinga hydrolysable polymer with an acid. Hydrolysable polymers useful hereininclude any polymers having a plurality of hydrolysable groups such thatwhen the polymer is reacted with acid the polymer becomes conductive. Inone aspect, the polyol comprises polyvinyl alcohol. The hydrolysablepolymer is poly(vinyl alcohol) (PVA), poly (vinyl acetate, poly (vinylalcohol co-vinyl acetate), poly (methyl methacrylate, poly (vinylalcohol-co-ethylene ethylene), poly (vinyl butyral-co-vinylalcohol-co-vinyl acetate), polyvinyl butyral, polyvinyl chloride, andany combination thereof. In another aspect, the hydrolysable polymer iserythritol, hydrogenated starch hydrolysates, isomalt, lactitol,maltitol, mannitol, sorbitol, xylitol, and any combination thereof.

In one aspect, the hydrolysable polymer has a molecular weight of fromabout 20,000 Da to about 300,000 Da, or about 20,000 Da, about 50,000Da, about 100,000 Da, about 150,000 Da, about 200,000 Da, about 250,000Da, or about 300,000 Da, where any value can be a lower and upperendpoint of a range (e.g., about 50,000 Da to about 100,000 Da). Inanother aspect, the hydrolysable polymer is poly(vinyl alcohol) (PVA)having a molecular weight of from about 20,000 Da to about 300,000 Da,or about 20,000 Da, about 50,000 Da, about 100,000 Da, about 150,000 Da,about 200,000 Da, about 250,000 Da, or about 300,000 Da, where any valuecan be a lower and upper endpoint of a range (e.g., about 50,000 Da toabout 100,000 Da).

The composite gel includes a conductive polymer in the form of apolyaryl amine. The polyaryl amine is produced by the polymerization ofan aryl amine. An aryl amine as defined herein as an aryl group with anamine group covalently bonded to the aryl group. As used herein, “arylgroup” is any carbon-based aromatic group including, but not limited to,benzene, naphthalene, etc. The term “aryl group” also includes“heteroaryl group,” which is defined as an aryl group that has at leastone heteroatom incorporated within the ring of the aromatic ring.Examples of heteroatoms include, but are not limited to, nitrogen,oxygen, sulfur, and phosphorus. In one aspect, the heteroaryl group isimidazole. The aryl group can be substituted or unsubstituted. The arylgroup can be substituted with one or more groups including, but notlimited to, alkyl, alkynyl, alkenyl, aryl, halide, nitro, amino, ester,ketone, aldehyde, hydroxy, carboxylic acid, or alkoxy. In one aspect,the aryl amine is aniline.

The aryl amine also includes aromatic compounds where the amine group ispart of the aromatic ring. An example of this includes pyrrole, wherethe NH group is part of the five-membered ring.

In one aspect, the polyaryl amine is a homopolymer of aniline or asubstituted aniline (e.g., alkyl, alkynyl, alkenyl, aryl, halide, nitro,amino, ester, ketone, aldehyde, hydroxy, carboxylic acid, or alkoxy). Inanother aspect, the polyaryl amine is a copolymer derived from two ormore different aryl amines. In another aspect, the polyaryl amine is acopolymer of aniline and a substituted aniline. In another aspect, thepolyaryl amine is polyaniline, poly(o-anisidine), poly(o-toluidine),poly(o-ethoxyaniline), poly(o-methoxyaniline), copolymerpoly(aniline-o-anisidine), copolymer poly(aniline-o-toluidine),copolymer poly(aniline-o-ethoxyaniline), poly(N-methyl aniline),sulfonated polyaniline, poly(o-phenylenediamine), or any combinationthereof.

The aryl group can be a fused aryl group consisting entirely of carbonatoms or, in other aspects, can include one or more heteroatoms (e.g.,oxygen nitrogen, sulfur, or any combination thereof). In one aspect, thefused aryl group has from 2 to 10 fused aromatic groups, or 2, 3, 4, 5,6, 7, 8, 9, or 10 aromatic groups, where any value can be a lower andupper end-point of a ranger (e.g., 2 to 8, 3 to 5, etc.). In one aspect,the fused aryl group includes naphthalene, anthracene, acenaphthene,acenaphthylene, fluorene, phenalene, phenanthrene, benzo[a]anthracene,benzo[a]fluorine, benzo[c]phenanthrene, chrysene, fluoranthene,tetracene, anthanthrene, benzopyrene, pyrene, benzo[a]pyrene,benzo[e]pyrene, benzo[b]fluoranthene, benzo[j]fluoranthene,benzo[k]fluoranthene, corannulene, coronene, dicoronylene,diindenoperylene, helicene, heptacene, hexacene, kekulene, ovalene,pentacene, perylene, picene, or tetraphenylenepentacene.

In one aspect, the polyaryl amine is a homopolymer of aniline or asubstituted aniline (e.g., alkyl, alkynyl, alkenyl, aryl, halide, nitro,amino, ester, ketone, aldehyde, hydroxy, carboxylic acid, or alkoxy). Inanother aspect, the polyaryl amine is a copolymer derived from two ormore different aryl amines. In another aspect, the polyaryl amine is acopolymer of aniline and a substituted aniline. In another aspect, thepolyaryl amine is polyaniline, poly(o-anisidine), poly(o-toluidine),poly(o-ethoxyaniline), poly(o-methoxyaniline), copolymerpoly(aniline-o-anisidine), copolymer poly(aniline-o-toluidine),copolymer poly(aniline-o-ethoxyaniline), poly(N-methyl aniline),sulfonated polyaniline, poly(o-phenylenediamine), or any combinationthereof.

The amine group in the aryl amine monomer can be unsubstituted orsubstituted with groups such as, for example, an alkyl group.

In one aspect, the composite gel is produced by admixing a hydrolysablepolymer, an aryl amine, an acid, and an oxidant. In one aspect, thecomposite gel is produced by

-   -   a. admixing the hydrolysable polymer and acid to produce a first        admixture;    -   b. admixing the oxidant with the first admixture to produce a        second admixture; and    -   c. admixing the aryl amine with the second admixture to produce        the composite gel.

In one aspect, the hydrolysable polymer and acid can be admixed invarying concentrations. In one aspect, the acid is HCI, H₂SO₄, H₃PO₄, orany combination thereof. In other aspect, the acid can be a weak acidsuch as, for example, citric acid. The acid can be a single acid or amixture of acetic acid, propionic acid, hydrochloric acid, hydrofluoricacid, phosphoric acid, sulfuric acid, formic acid, benzoic acid,hydrofluoric acid, nitric acid, phosphoric acid, sulfuric acid,tungstosilicic acid hydrate, hydriodic acid, carboxylic acids,dicarboxylic, tricarboxylic, oxalic acid, hexacarboxylic acid, citricacid, p-camphor sulfonic, FeCl₃ and polyacrylic, tartaric acid, oxalicacid, or any combination thereof.

In one aspect, the first admixture is produced by admixing 1 g to 10 gof hydrolysable polymer (e.g., polyvinyl alcohol) in 100 mL of HCI,where the concentration of HCI is from about 0.5 M to about 1.5 M. Inone aspect, the first admixture is heated at a temperature of from about50° C. to about 100° C. for 1 hour to 12 hours.

An oxidant is next added to the first admixture to produce a secondadmixture. A single oxidant or mixtures of two or more oxidants can beused. Examples of oxidants useful here include, but are not limited to,ammonium persulfate, ferric chloride, aluminum nitrate, ammoniumdichromate, ammonium peroxydisulphate, barium nitrate, bismuth nitrate,calcium hypoperchlorate, copper (II) nitrate, cupric nitrate, ferricnitrate, hydrogen peroxide, lithium hydroxide monohydrate, magnesiumnitrate, magnesium perchlorate, potassium chlorate, potassiumdichromate, potassium permanganate, sodium hypochlorite, sodiumperiodate, zinc nitrate hydrate, nitric acid, sulfuric acid, perchloricacid, ammonium nitrate, silver nitrate, benzoyl peroxide,tetranitromethane, sodium perchlorate, potassium perchlorate, potassiumpermanganate, potassium persulfate, sodium nitrate, potassium chromate,or any combination thereof. In one aspect, the oxidant is added to thefirst admixture produced by admixing 1 g to 10 g of hydrolysable polymer(e.g., polyvinyl alcohol) in 100 mL of HCI, where the concentration ofHCI is from about 0.5 M to about 1.5 M.

Once the second admixture is produced, the aryl amine is added toproduce the aryl amine in situ. In one aspect, the aryl amine isaniline, where polyaniline is produced in situ. In another aspect, thearyl amine is pyrrole, where polypyrrole is produced in situ. TheExamples provide nonlimiting procedures for making the composite gelsuseful herein. Here, the polyaryl amine is homogeneously dispersedthroughout the composite gel.

In certain aspects, a photosensitive dye can be incorporated in thecomposite gels described herein. For example, the photosensitive dye canbe included in the first or second admixture described above. Examplesof photosensitive dyes useful herein include, but are not limited to, anorganic dye, a porphine-based dye, or a ruthenium-based dye.

The composite gels described herein are easy to produce at a low-cost,which makes them suitable in a number of different applicationselectrochromic devices, supercapacitors, solar cells, and hybridphotoactive supercapacitors. For example, hybrid solarcell-supercapacitors can be used in self-powered wireless sensors,particularly for structural health monitoring systems (SHMS). In anSHMS, a large number (a few thousand) of wireless sensors are installedover the body of a structure (e.g., bridges or buildings) to measure andtransmit vibration, temperature, and corrosion rate. As a practicalsolution, the sensors can be designed to harvest solar energy.Considering the number of required sensors for a single structure, acompact and low-cost device with the dual functions of energy harvestingand storage can dramatically reduce the sensors cost and provide apractical solution for constant monitoring of the structure's health.The solar cells with the composite gels described herein provide asolution to this long felt need. Additionally, low-cost and moreefficient devices can be designed and fabricated by customizing thecomposite gels described herein by adding other elements such as dyes ornanoparticles.

In one aspect, the electrochemical cells described herein can be used asa solar cell for harvesting and storing solar energy. In one aspect, thefirst electrode is a working electrode and the second electrodefunctions as the counter electrode, wherein the composite gel ispositioned between the electrodes. In one aspect, the working electrodeis a transparent electrode. In one aspect, the working electrode is alayer of glass that is coated with a conductive coating such as forexample, indium tin oxide (ITO) or fluorine-doped tin oxide (FTO). Insome aspects, the counter electrode includes a layer of highly porousactivated carbon paper.

Aspects

Aspect 1. An electrochemical cell comprising

-   -   a. a first electrode having a first surface and second surface;    -   b. a second electrode having a first surface and second surface;        and    -   c. a composite gel positioned between the first electrode and        the second electrode, wherein the composite gel comprises a        polyaryl amine, an electrolyte, and an oxidant.

Aspect 2. The electrochemical cell of Aspect 1, wherein the electrolytecomprises the reaction product between a hydrolysable polymer and anacid.

Aspect 3. The electrochemical cell of Aspect 2, wherein the hydrolysablepolymer comprises poly(vinyl alcohol) (PVA), poly (vinyl acetate, poly(vinyl alcohol co-vinyl acetate), poly (methyl methacrylate, poly (vinylalcohol-co-ethylene ethylene), poly (vinyl butyral-co-vinylalcohol-co-vinyl acetate), polyvinyl butyral, polyvinyl chloride, andany combination thereof.

Aspect 4. The electrochemical cell of Aspect 2, wherein the hydrolysablepolymer has a molecular weight of from about 20,000 Da to about 300,000Da.

Aspect 5. The electrochemical cell of Aspect 2, wherein the hydrolysablepolymer is poly(vinyl alcohol) a molecular weight of from about 20,000Da to about 300,000 Da.

Aspect 6. The electrochemical cell in any one of Aspects 1 to 5, whereinthe polyaryl amine is a homopolymer of aniline or a substituted aniline.

Aspect 7. The electrochemical cell in any one of Aspects 1 to 5, whereinthe polyaryl amine is a copolymer derived from two or more differentaryl amines.

Aspect 8. The electrochemical cell in any one of Aspects 1 to 5, whereinthe polyaryl amine is a copolymer of aniline and a substituted aniline.

Aspect 9. The electrochemical cell in any one of Aspects 1 to 5, whereinpolyaryl amine comprises polyaniline, poly(o-anisidine),poly(o-toluidine), poly(o-ethoxyaniline), poly(o-methoxyaniline),copolymer poly(aniline-o-anisidine), copolymerpoly(aniline-o-toluidine), copolymer poly(aniline-o-ethoxyaniline),poly(N-methyl aniline), sulfonated polyaniline,poly(o-phenylenediamine), polypyrrole, or any combination thereof.

Aspect 10. The electrochemical cell in any one of Aspects 1 to 9,wherein the composite gel is produced by admixing a hydrolysablepolymer, an aryl amine, an acid, and an oxidant.

Aspect 11. The electrochemical cell in any one of Aspects 1 to 10,wherein the composite gel is produced by

-   -   a. admixing the hydrolysable polymer and acid to produce a first        admixture;    -   b. admixing the oxidant with the first admixture to produce a        second admixture; and    -   c. admixing the aryl amine with the second admixture.

Aspect 12. The electrochemical cell of Aspect 10 or 11, wherein thehydrolysable polymer comprises polyvinyl alcohol.

Aspect 13. The electrochemical cell in any one of Aspects 10 to 12,wherein the aryl amine comprises aniline or a substituted aniline.

Aspect 14. The electrochemical cell in any one of Aspects 10 to 13,wherein the acid comprises acetic acid, propionic acid, hydrochloricacid, hydrofluoric acid, phosphoric acid, sulfuric acid, formic acid,benzoic acid, hydrofluoric acid, nitric acid, phosphoric acid, sulfuricacid, tungstosilicic acid hydrate, hydriodic acid, carboxylic acids,dicarboxylic, tricarboxylic, oxalic acid, hexacarboxylic acid, citricacid, p-camphor sulfonic, FeCl₃ and polyacrylic, tartaric acid, oxalicacid, or any combination thereof.

Aspect 15. The electrochemical cell in any one of Aspects 10 to 14,wherein the oxidant comprises ammonium persulfate, ferric chloride,aluminum nitrate, ammonium dichromate, ammonium peroxydisulphate, bariumnitrate, bismuth nitrate, calcium hypoperchlorate, copper (II) nitrate,cupric nitrate, ferric nitrate, hydrogen peroxide, lithium hydroxidemonohydrate, magnesium nitrate, magnesium perchlorate, potassiumchlorate, potassium dichromate, potassium permanganate, sodiumhypochlorite, sodium periodate, zinc nitrate hydrate, nitric acid,sulfuric acid, perchloric acid, ammonium nitrate, silver nitrate,benzoyl peroxide, tetranitromethane, sodium perchlorate, potassiumperchlorate, potassium permanganate, potassium persulfate, sodiumnitrate, potassium chromate, or any combination thereof.

Aspect 16. The electrochemical cell in any one of Aspects 10 to 15,wherein the composite gel further comprises photosensitive dye.

Aspect 17. The electrochemical cell of Aspect 16, wherein thephotosensitive dye comprises an organic dye, a porphine-based dye, or aruthenium-based dye.

Aspect 18. The electrochemical cell in any one of Aspects 1 to 17,wherein the composite gel has a thickness of from about 50 μm to about500 μm.

Aspect 19. The electrochemical cell in any one of Aspects 1 to 18,wherein the composite gel has a specific capacitance of from about 300mF/g to about 700 mF/g.

Aspect 20. The electrochemical cell in any one of Aspects 1 to 19,wherein the first electrode and second electrode are composed of thesame material.

Aspect 21. The electrochemical cell in any one of Aspects 1 to 20,wherein the first electrode and second electrode are composed of thesame material.

Aspect 22. The electrochemical cell in any one of Aspects 1 to 20,wherein the first electrode comprises a transparent material.

Aspect 23. The electrochemical cell in any one of Aspects 1 to 20,wherein the first electrode comprises glass or fluorine-doped tin oxideglass.

Aspect 24. The electrochemical cell in any one of Aspects 1 to 20,wherein the second electrode comprises porous carbon.

Aspect 25. The electrochemical cell in any one of Aspects 1 to 20,wherein the first electrode comprises porous carbon, platinum, or TiO₂,and the second electrode comprises porous carbon, platinum, or TiO₂.

Aspect 26. The electrochemical cell in any one of Aspects 1 to 25,wherein the first electrode comprises fluorine-doped tin oxide glasswith a coating comprising TiO₂ or platinum on the first surface, thesecond electrode comprises fluorine-doped tin oxide glass with a coatingcomprising TiO₂ or platinum on the first surface, or both the firstelectrode and second electrode comprises fluorine-doped tin oxide glasswith a coating comprising TiO₂ or platinum on the first surface.

Aspect 27. The electrochemical cell in any one of Aspects 1 to 26,wherein the electrochemical cell further comprises a separator adjacentto the first surface of the first electrode, a separator adjacent to thefirst surface of the second electrode, or a separator adjacent to thefirst surface of the first electrode and second electrode.

Aspect 28. A device comprising the electrochemical cell in any one ofAspects 1 to 27.

Aspect 29. The device of Aspect 28, wherein the device comprises anelectrochromic device, a supercapacitor, a solar cell, or a hybridphotoactive supercapacitor.

Now having described the aspects of the present disclosure, in general,the following Examples describe some additional aspects of the presentdisclosure. While aspects of the present disclosure are described inconnection with the following examples and the corresponding text andfigures, there is no intent to limit aspects of the present disclosureto this description. On the contrary, the intent is to cover allalternatives, modifications, and equivalents included within the spiritand scope of the present disclosure.

EXAMPLES

The following examples are put forth so as to provide those of ordinaryskill in the art with a complete disclosure and description of how thecompounds, compositions, articles, devices and/or methods claimed hereinare made and evaluated, and are intended to be purely exemplary of thedisclosure and are not intended to limit the scope of what the inventorsregard as their disclosure. Efforts have been made to ensure accuracywith respect to numbers (e.g., amounts, temperature, etc.), but someerrors and deviations should be accounted for. Unless indicatedotherwise, parts are parts by weight, temperature is in ° C. or is atambient temperature, and pressure is at or near atmospheric.

EXPERIMENTAL SECTION

Materials. All chemical materials, including multi-walled carbonnanotubes (MWCNTs), sodium dodecyl benzenesulfonate (SDBS), polyvinylalcohol (PVA), hydrochloric acid (HCI), aniline, and ammonium persulfate(APS) were purchased from Sigma-Aldrich and used as received without anyfurther purification. FTO electrodes were purchased from HuanyuInstrument (China) with 1.66 mm thickness and 12 Ω·cm-2 sheetresistance. Pt-coated FTO conductive electrodes (2.0 cm×2.0 cm) and TiO₂coated FTO electrodes (2.0 cm×2.0 cm with 6 mm×6 mm active area—TiO₂coated part) were purchased from Solaronix. Two pieces of glassy carbons(25×25×3 mm3) were purchased from SPI Supplies. The paper substratesused for making the electrodes were standard lettersize copy paper fromOffice Depot.

Electrodes Preparation. Porous carbon electrodes were made using inhouseprepared MWCNT-based ink on the copy papers. Following the instructiondeveloped by Hu et al., the ink was made by first mixing 300 mg of CNTsand 150 mg of SDBS in 30 mL of deionized (DI) water. Then, the solutionwas sonicated for 30 min using a probe sonicator at 30 W and 40 Javerage power and energy, respectively. The conductive ink solution wasused to make the electrodes by drop casting 1 mL on the surface of apiece of a paper (4.0 cm×7.0 cm) and drying in a vacuum oven for 30 minat 120° C. The process was repeated three times to make the electrodesconductive enough. The conductive paper sheet was cut in rectangularpieces with the surface area of 4.0 cm×0.8 cm or 4.0 cm×0.6 cm, aselectrodes for supercapacitors and photoactive supercapacitor devices.The thickness of the CNTs based electrodes was 150 μm. Additionally, theconductivity of the electrodes was measured to be 98 Ω·cm⁻¹ using acustom made four-probe setup connected to a Keithley (2602) sourcemeterunit. Before using, FTO, Pt, FTO-TiO₂ and glassy carbon electrodes werecleaned by rinsing with DI water, sonicating in DI water for 5 min, andsonicating in methanol and then in ethanol each for 5 min. The cleanedelectrodes were dried under hot air flow.

Composite Gel Preparation. The gel composite was synthesized following arecipe from other publications. First, PVA-HCI gel electrolyte was madeby dissolving 5 g of PVA in 100 mL of 1 M HCI in a beaker. Then, thesolution was stirred continuously and heated at 75° C. for 6 hrs at aspeed of 400 rpm. After that, 30 ml solution of 0.1 M APS in 1 M HCI wasadded to the PVA-HCI solution at room temperature and stirred for 30 minat 600 rpm. At last, the composite gel was made by adding 3 ml ofaniline to the PVA-HCI-APS at room temperature and stirred for 12 hrs.The composite gel polymer electrolyte was kept in a beaker (covered by apiece of Parafilm) at room temperature for at least a week beforefabrication of the devices.

Device Fabrication. Devices were made by coating the entire surface ofone of the electrodes with the composite gel, putting one layer of afiberglass mesh (mesh thickness of 270 μm) or a Parafilm frame (130 μmthick) as separator, and putting the second electrode on the mesh andpressing them together with binder clips. Mesh separators were used forthe device with the glassy carbon electrodes and the supercapacitor (CNTbased electrodes). In the supercapacitor, the gel covered only 8 mm×8 mmof each electrode. Frames were cut from a Parafilm and used between thetwo electrodes in the electrochemical cell. The effective area coveredby the gel in the electrochemical cell and the hybrid device was only 6mm×6 mm (i.e., TiO₂ coated area on FTO). The gel covered area in theelectrochromic device was 2.0 cm×1.5 cm.

Electrical and Electrochemical Measurements. VersaSTAT 4 potentiostatwith two-terminals configuration was used to measure the electrochemicaland electrical tests, including CV, EIS, galvanostatic method, opencircuit voltage, and short circuit current all in the two-probeconfiguration. All CVs were conducted at 50 mV·s⁻¹ scan rate. Multiplecycles were tested, and the last cycle of each experiment is reported inthis work, except for the device with the glassy carbon electrodes thatboth the first and last cycle data is reported. All EIS studies weredone at 0.0 V DC bias with an AC voltage amplitude of 20 mV for afrequency range of 0.1 Hz to 10 kHz. All the electrochemicalmeasurements were carried out at room temperature. More specifically,the measurements for the supercapacitor and electrochromic devices wereperformed at ambient light in the lab. However, the hybrid photoactivesupercapacitor and the electrochemical cell were placed in a dark boxconnected via an optical fiber to a solar simulator (RST, Radiant SourceTechnology) with an output power intensity of 80 mW·cm-2, which wasequipped with an internal AM 1.0 optical filter. The experimental setup,including the dark box and the shutter mechanism, was designed toeliminate the effect of ambient light in the experiment. UV-Vis spectraand the transmittance data were recorded by a Thermo ScientificEvolution 201/220 UV-Visible Spectrophotometer. FTIR and Raman analysiswere done by using PerkinElmer Spectrum 100 FT-IR and LabRAM HREvolution, respectively.

Results and Discussion

The composite gel material was synthesized by first mixing PVA andhydrochloric acid (HCI) in water. In two steps, ammonium persulfate(APS) and monomer ‘aniline’ were added. APS and HCI reacted with anilineto produce PANI which was uniformly distributed in the PVA gelelectrolyte. Chemically salt (ES) which is naturally green in color.

The optical absorption of the composite gel with PANI was studied andcompared with the gels made from only PVA, PVAHCI, and PVA-HCI-APS. Asshown in FIG. 1A, the gels without PANI were all transparent, but theabsorption spectrum of the gel containing PANI confirmed the formationof the ES form of the polymer. The relatively broad absorption peakaround 775 nm corresponds to the energy gap between the valence andpolaron bands, and the peak at 350 nm is attributed to the transitionfrom the valence band to the conduction band. Also, the shoulder at 440nm is ascribed to the polaron to the conduction band transition, asshown in inset FIG. 1 .a. The FTIR study was done to learn about theinteraction of the PVA polymer matrix with APS and PANI. Afternormalization in the range of 650-4000 cm-1, the FTIR spectra (FIG. 1B)showed several transmittance peaks for PVA, PVA-HCI, PVA-HCI-APS, andPVA-HCI-APSPANI. The wide absorption at the wavenumber from 3700-3000cm-1 is due to the symmetry of the stretching vibration of hydroxyl inPVA. Also, NH stretching vibration of the —C6H4NHC6H4- groups of PANI ispresent in this region.[26] The band at 2950-2660 cm⁻¹ is related to C—Hstretching in the alkyl group.

The above broad band nature is extended up to nearly 2500 cm⁻¹ inpresence of PANI. In the wavenumber range, 2950-2600 cm⁻¹ only oneshoulder was observed in the FTIR spectrum of PVA while in presence ofPANI, two shoulders appeared in this region with relatively highprominent feature. These well-defined shoulders at around 2950 and 2637cm-1 are possibly due to the strong H-bonding of hydroxyl group of PVAwith PANI in addition to the stretching vibrations related to C—H. Tounderstand the interaction of PVA with PANI during the reactionprogress, the band at around 1000-1150 cm⁻¹ of PVA should be preciselynoted in presence of acid, APS and PANI. The band at 1100 cm⁻¹ may beattributed to O—H deformation and C—O stretching vibration of secondaryalcohol of PVA in PVA as well as in PVA+HCI. In the presence of APS thisband apparently splits, and a new band appears at around 1050 cm⁻¹ whichis possibly due to the start of oxidation of PVA. Intensity of this banddecreases in presence of PANI. During oxidation the stretching vibrationof C═C becomes more symmetric and it shows at ˜1650 cm⁻¹. The bands at1283 cm⁻¹ (assigned as C—N stretching due to the linkage of APS withPVA), 1105 cm-1 (C—O stretching) and 820 cm-1 (C—S stretching) are forPVA-APS gel-based electrolyte. Two main peaks at around 1450 cm⁻¹ and1283 cm⁻¹ occur for C—C and C—N stretching modes, their shapes differalong with intensity ratio being opposite in presence of PANI.Broadening of these bands usually occur due to differentiation of theirbond order. In addition, the expanded intensities of C—O and C—Sstretching of PANI composite gel electrolyte in comparison to the othermaterials are apparent which also verifies the interaction of PANI withPVA and APS materials.

For further investigation, Raman spectra were taken for all similarsystems to understand the interaction between PVA and PANI. The band at1080 cm⁻¹ of PVA is assigned as O—H bond deformation. In presence ofHCI, line broadening occurs possibly for cross linking of PVA, whichshifts towards lower wavenumber with disappearing nature to supportoxidation by APS. On the other hand, in presence of PANI, it shifts tohigher wavenumber, 1130 cm⁻¹ along with the development of threecharacteristic bands due to the stretching of (i) C—N+. (ii) imine (iii)and partially charged imine groups. The band for C—N+. appears at around1330 cm⁻¹ with splitting pattern having peaks at 1320 and 1340 cm⁻¹which are possibly for polaron and bipolaron effects. The stretchingvibration of C—O of PVA after interaction with PANI may also contributeto this 1340 cm⁻¹ band. The Raman spectrum of PVA shows a band at around1360 cm⁻¹ which appears at lower wavenumber, 1340 cm-1 for interactionwith PANI. The contribution of benzenoid and quinoid structures of PANIwas studied by Raman spectra (FIG. 1C). Band shift (a mixed mode of theC═N and CH═CH stretching vibrations) due to the quinoid structureappears around 1485-1471 cm⁻¹. In addition, other band shifts at 1150,950, 870 due to C—H in-plane bending and C—N—C of the benzene ring arerelated to both polaronic and bipolaronic structures in the PANI in thepresence of HCI and PVA.

To study the electrical properties, a layer of the PVA-PANI gel(thickness=˜270 μm) was sandwiched between two glassy carbon (GC)electrodes with an area of 25×25 mm². The cell was then tested via thecyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS)methods. The redox peaks in the CV result (FIG. 1D) and nature compleximpedance (FIG. 1E) show that the PANI composite gel electrolyte has acharge storage property like a pseudocapacitor. The magnitude of thecapacitance was estimated from the CV data to be 38.6 mF, which is twoorders of magnitude higher than the estimated double layer capacitancein a device with non-porous electrodes and surface area of 25×25 mm2.While the glassy carbon is not a redox active material and the storagecapacitance in a gel without the conducting polymer is negligible, thesymmetric redox peaks in the CV loop suggest a pseudocapacitive chargestorage mechanism in the bulk gel electrolyte due to the presence ofPANI. Considering the mass of the gel, the specific capacitance (Cgel)of the composite gel has been calculated to be 428.9 mF g-1. Themechanism of charge storage in the volume of the gel can be explainedthrough the change in the oxidation state of PANI (inset FIG. 1D)between leucoemeraldine salt (LS) and ES by removing/adding electron andproton (H+) pairs in a reversible redox reaction:

The reversibility of the reactions and the stability of the gel in anon-sealed device was confirmed after 1000 cycles in the CV with <1%change in the capacitance. Since the conducting polymer is dispersedinside the bulk gel, the occurrence of the redox reaction implies thecapability of the composite gel to conduct both electronic and ioniccharge. The profile of the Nyquist response from the EIS result (FIG.1E) confirms this feature by showing a pure constant phase elementresponse that can be modeled as distributed elemental capacitances andresistors in the bulk gel (FIG. 1F). In this model, each monomer mimicsa capacitor, C, that can be charged or discharged by receiving/donatingan electron-H+ pair. Rion and Rele represent the elemental resistors forionic and electronic charge transport through the composite gel,respectively.

Since one expects the formation of double layer charges at theinterfaces between the gel and the electrodes, two capacitors (Cdl1 andCdl2) are considered in the model. The resistance of the electrodes isalso shown as series resistors Rs1 and Rs2. Due to the distributedcapacitors in the volume of the gel, when a voltage is applied acrossthe gel layer, a progressive charging process is expected by pumpingpositive and negative charges from the electrodes until all theelemental capacitances are charged.

Recognizing this unique capability of storing charge in the PANIcomposite gel, a simple supercapacitor device was fabricated with twocarbon nanotubes (CNTs) based porous electrodes and the PANI basedcomposite gel as the electrolyte. FIGS. 2A and 2B show a schematic and apicture of the supercapacitor with the gel layer thickness of ˜270 μm.In FIG. 2C, the CV result from the device with the PVA-HCI-APS-PANI gelelectrolyte is compared with that in a similar device with an acidic gelof PVA-HCI. The results clearly show the advantage in employing bothionic and electronic conductivity in the composite gel to store chargesin the volume of the electrolyte as well as at the double layers. Theabsence of the redox peaks in the CV result from the PANI composite gelimplies domination of the storage via the double layer charges due tothe high porosity of the electrodes. Supercapacitor devices with gelelectrolytes with and without the conducting polymer was further studiedvia the EIS and galvanostatic charging methods. Specifically, thegalvanostatic test showed an equivalent series resistance (ESR) of ˜83Ω.Considering the poor conductivity of the CNT electrodes, application ofmore conductive electrodes with current collectors would reduce ESRsignificantly.

The overall capacitance of the device with the PANI-based gel wasestimated from the CV result to be 48 mF which corresponds to 3.33 Fg-1(specific capacitance) based on the mass of CNTs on the electrodes. Thespecific capacitance can be significantly increased by optimizing theelectrode material and structure. For instance, much higher capacitancescan be achieved by using composite redox active materials with graphene,conducting polymers, and molybdenum disulfide for the electrodes. Withthe mechanism of charge storage inside the gel volume, potentially,devices can be fabricated with higher energy and power densities thanconventional devices without this feature. The concept of usingsmall-molecule based redox active materials in the electrolyte of adevice for partial charge storage has been reported before. In thecomposite gel, PANI is acting as the redox material and thehydrogenation/dehydrogenation of PVA adds to the storage capacity of thebulk gel. Considering the low cost of the gel material and simplicity indevice fabrication, the PANI composite gel is potentially suitable forfabricating high capacitances, low cost, and flexible supercapacitors.

The UV-vis study of the PANI composite gel (FIG. 1A) showed lightabsorption by PANI. Therefore, the feasibility of harvesting solarenergy by the composite gel was studied in a DSSC-like device. As shownin FIGS. 3A and 3B, the gel was placed between two electrodes: a TiO2coated FTO (fluorine doped tin oxide) as the anode and a Pt-coated FTOas the cathode. In this configuration, dye material was not used, andthe gel acted both as the electrolyte and photoactive layer in whichPANI (ES form) was the photoactive material and PVA mesh with ionsserved as the electrolyte. The current-voltage characteristics of thedevice were measured both under dark and under simulated sunlightconditions. The J-V characteristics in FIG. 3C clearly show thegenerated power under illumination. From the results, the device wasfound to have an open circuit voltage (VOC) of 0.48 V and a shortcircuit current density (JSC) of 0.12 mA·cm-2. However, the fill factorand overall conversion efficiency were relatively low compared toconventional DSSCs with a separate layer of dye materials and liquidelectrolytes. This can be further addressed by adding dye materials tothe gel.

Since the composite gel demonstrated both energy storage and solarenergy harvesting capabilities, we designed and tested a hybrid devicefor concurrent harvesting and storage in a single two-terminal device(i.e., photoactive supercapacitor). The hybrid device was made as beforewith a single layer of the gel between two electrodes: a FTO-TiO₂ and aporous CNT-based electrode (FIGS. 4A and 4B).

FIG. 4C shows the CV measurements under dark conditions. The loopverifies the internal storage capacity. A part of this storage effect isdue to the double charges at the electrode electrolyte interfaces.However, the redox peaks imply additional charge storage in apseudocapacitive form, occurring inside the volume of the composite gelelectrolyte due to the existence of PANI and PVA. From the electricalresponse of the cell in the dark (FIG. 4C), the specific capacitance ofthe cell was calculated to be 1.53 Fg⁻¹. Additional characterization ofthe photoactive supercapacitor through the galvanostatic test showed anequivalent series resistance (ESR) of ˜120Ω.

To study the capability of the device for solar energy harvesting, theopen circuit voltage of the cell was monitored under dark and lightconditions. As shown in FIG. 4D, the voltage across the cell wasincreased gradually from 92 mV (dark) to 137 mV in 400 s under lightconditions. The gradual voltage change is due to the storage property ofthe device. The trend in the voltage change suggests that longerillumination time could result in a larger voltage increase beforereaching a saturated level when the internal capacitor is fully charged.After cessation of the light, the voltage did not return to its initialdark value. Instead, the slow change in the voltage under darkconditions (i.e. 10 mV drop in 600 s) shows the capability of the gel toretain the charge for a relatively long time. This implies low leakagecurrent in the discharge process.

Additionally, the short circuit current in the cell was studied underalternating 20 s of dark and light pulses (FIG. 4E). The non-zerocurrent in the dark is from the stored charges. However, the currentshowed an increase of ˜0.5 μA when the cell was illuminated by the solarsimulator. The low current in the dark is because of the large internalresistance. It should be mentioned that the conventional J-Vcharacteristics do not reflect the full capability of the cell due tothe large storage effect and the low photocurrent. Therefore, no attemptwas made to measure the efficiency and the fill-factor of the device.The majority of hybrid devices were made by integrating a DSSC with asupercapacitor in one package and sharing one of the electrodes of eachcell to make a three-terminal hybrid device. For practical applications,a two terminal hybrid device is potentially more efficient. Almost allreported two terminal hybrid devices have a multilayer structure for thephotoactive layer with an electrolyte and a porous counter electrode.The above described single layer device composed of a gel as thephotoactive layer, energy storage media, and electrolyte is morepromising for the development of low-cost and dry photoactivesupercapacitors. Additionally, our preliminary results show that addinga dye material to the composite gel can enhance the energy harvesting inthe gel.

The synthesized gel was also tested for electrochromic applications byfabricating a device with two FTO electrodes and a single active layerof the PANI composite gel in between (FIG. 5A). As shown in FIG. 5B, thegel was semi-transparent when PANI was in its ES form. The CV study ofthe cell (FIG. 5C) showed an almost symmetrical response with redoxpeaks around ±1.5 V and around ±0.38 V. As the voltage of the cell waschanging, we noticed that for applied voltages larger than 1.5 V,(|Vapplied|>1.5 V), the color of the gel changed to dark blue. However,when the voltage was scanned to a lower magnitude, the gel becametransparent at ˜0.5 V. To study the two modes of operation, the voltagewas pulsed between 0.0 V and 2.0 V every 20 s. As shown in FIG. 5D, thecurrent through the cell showed a transient response with a steady statecurrent of ˜50 mA and 0.0 mA at the dark and transparent modes,respectively. The color change in the sample is clearly seen in FIG. 5B.After applying the last voltage pulse at 2.0 V, the cell was operatedunder open circuit conditions (FIG. 5E). The gradual voltage changeoccurred with a slow color change to green, while the color changebetween the transparent and dark modes under the applied pulses wasalmost instantaneous. The transparency test results show 64%transmittance around 564 nm at 0.0 V, while the transmittance was almostzero at 2.0 V for the entire range of the spectrum (FIG. 5F).

As shown in FIG. 6A, the step-by-step adding chemicals have resulted inthe formation of PANI-emeraldine salt (ES) which is green in color. Asexplained, the mechanism of charge storage in the gel is due to thechange in the oxidation state of PANI in the bulk gel. In thesupercapacitor device, the oxidation state was changed between ES and LSstates by adding or removing electron-proton (H+) pairs. However asshown in FIG. 6B, the oxidation state of PANI can also be changed toemeraldine base (EB) by removing protons (H+) and dedoping the polymer.This process is reversible, and the polymer can get back to the ES formthrough a protonation process. Transition from LS to ES and then EBunder sufficiently large voltages across the gel was confirmed in theelectrochromic experiments. Not only the CV result (FIG. 5C) implied thechange in the oxidation state, but also the color change was a clearevidence as EB has a dark blue color and LS is fade yellow totransparent in color.

The fact that the oxidation state of the conducting polymer inside thevolume of the gel can be changed suggests existence of both ionic andelectronic conductions through the gel. In this regard, the compositegel is different than regular gel electrolytes with only ionic chargetransport. This unique property of conducting two different types ofcharges can also explain the observed photovoltaic effect in the bulkgel. The energy diagram of the solar cell and the hybrid photoactivesupercapacitor is shown in FIG. 6C. In the composite gel, ES form ofPANI absorbs light and generates an excited state. The photogeneratedelectrons can be transferred to the conduction band of TiO2 and aregeneration process by the ionic mediators (S2O82-+2e-⇄2SO42-) replacethe lost electrons in PANI. In the last step, charge exchange occursbetween the mediators and the cathode (i.e., Pt or CNT-based electrode).The detail reactions are explained as below:

The device with the Pt cathode responded like a DSSC with a negligiblecharge storage effect. This can be due to the catalytic property of Ptthat facilitates the charge circulation via the mediator forregeneration of PANI into its ES state. However, the weak of catalyticproperty in CNTs can affect the regeneration process in PANI and convertit to the pernigraniline form after losing the photoexcited electronsand H+ ions (Emeraldine+hv→e−+H++ pernigraniline). Losing a negative(e−) and a positive (H+) charge results in a higher energy mode in PANIwhich was observed as gradual increase in the open circuit voltage ofthe hybrid photoactive supercapacitor. The difference in the energystructure of PANI in the Emeraldine and pernigraniline are shown in FIG.6D.

The change in the oxidation state can also explains the charge stabilityin the device. Since at the pernigraniline state the electronicconductivity in the polymer is substantially lower than that in the ESform, the recombination rate between electronic and ionic charges wouldbe considerably lower, resulting in a stable form of charge storage indark as it was observed in FIG. 4D.

Although the results clearly show the feasibility of using the compositegel for fabricating various low-cost devices by simply putting a layerof the gel between two electrodes, the composite can be furthercustomized for different applications. For example, for solar cells orphotoactive supercapacitors, a dye material could be added to the gel toenhance the light absorption. This is particularly necessary as PANI inits LS state is semi-transparent. Also, for long operational lifetime ofdevices appropriate sealing and packaging is required.

CONCLUSION

A facile and low-cost procedure for preparing a new composite materialof gel electrolyte is described. The electrical and electrochemicalbehavior of the composite gel was investigated for application toelectrochromic devices, supercapacitors, solar cells, and hybridphotoactive supercapacitors. While all the devices studied in this workare traditionally electrochemical devices, application of the compositegel with both ionic and electronic conductivity between two electrodesdemonstrates a different type of cell with a single layer material beingactive in its entire volume. Potentially, low-cost and more efficientdevices can be designed and fabricated by customizing the composite gelby adding other elements such as dyes or nanoparticles. An additionalstudy is needed to explore the impact of materials and concentrations onthe energy storage and photovoltaic properties of the devices.

It should be emphasized that the above-described embodiments of thepresent disclosure are merely possible examples of implementations setforth for a clear understanding of the principles of the disclosure.Many variations and modifications may be made to the above-describedembodiment(s) without departing substantially from the spirit andprinciples of the disclosure. All such modifications and variations areintended to be included herein within the scope of this disclosure andprotected by the following claims.

1. A method comprising: structuring a first material stack by disposinga first material separator layer dimensioned as a first mesh or a firstframe on a first electrode layer; placing a layer of a composite gelonto the first material separator layer, wherein the composite gelincludes a polyaryl amine, an electrolyte, and an oxidant and has aspecific capacitance with a value from about 300 mF/g to about 700 mF/g;and disposing a second material stack, which contains a second materialseparator layer dimensioned as a second mesh or a second frame and asecond electrode layer, in contact with the layer of the composite gelsuch as to sandwich the second material separator layer between thelayer of the composite gel and the second electrode layer whileestablishing physical contact between the layer of the composite gel andboth the second material separator layer and the second electrode layer.2. A method according to claim 1, comprising forming said composite gelbased on a product of a reaction between a hydrolysable polymer and anacid.
 3. A method according to claim 2, wherein said forming includesforming the composite gel that includes a photo-sensitive dye.
 4. Amethod according to claim 2, wherein the hydrolysable polymer comprisesany of poly(vinyl alcohol) (PVA), poly (vinyl acetate, poly (vinylalcohol co-vinyl acetate), poly (methyl methacrylate, poly (vinylalcohol-co-ethylene ethylene), poly (vinyl butyral-co-vinylalcohol-co-vinyl acetate), polyvinyl butyral, polyvinyl chloride, and acombination thereof.
 5. A method according to claim 2, wherein thehydrolysable polymer has a molecular weight from about 20,000 Da toabout 300,000 Da.
 6. A method according to claim 2, wherein thehydrolysable polymer is poly(vinyl alcohol) a molecular weight fromabout 20,000 Da to about 300,000 Da.
 7. A method according to claim 1,comprising forming said composite gel as a product of admixing ahydrolysable polymer, an aryl amine, an acid, and an oxidant.
 8. Amethod according to claim 1, comprising forming said composite gel by(8A) admixing the hydrolysable polymer and acid to produce a firstadmixture; (8B) admixing the oxidant with the first admixture to producea second admixture; and (8C) admixing the aryl amine with the secondadmixture.
 9. A method according to claim 1, wherein the structuringsaid first material stack includes forming the first material stackincludes at least one of porous carbon, platinum, and TiO₂.
 10. A methodaccording to claim 1, wherein the structuring said first material stackincludes using glass or fluorine-doped tin-oxide glass as part of saidfirst material stack.
 11. A method according to claim 1, wherein theplacing includes bringing in contact with said composite gel said secondelectrode that comprises fluorine-doped tin oxide glass with a coatingon a surface of said glass, the coating including TiO₂ or platinum. 12.A method according to claim 1, wherein said disposing the first materialseparator layer dimensioned as the first mesh or the first frame on thefirst electrode layer includes disposing a fiberglass mesh or a parafilmframe on the first electrode layer.
 13. A method according to claim 1,wherein the oxidant comprises any of ammonium persulfate, ferricchloride, aluminum nitrate, ammonium dichromate, ammoniumperoxydisulphate, barium nitrate, bismuth nitrate, calciumhypoperchlorate, copper (II) nitrate, cupric nitrate, ferric nitrate,hydrogen peroxide, lithium hydroxide monohydrate, magnesium nitrate,magnesium perchlorate, potassium chlorate, potassium dichromate,potassium permanganate, sodium hypochlorite, sodium periodate, zincnitrate hydrate, nitric acid, sulfuric acid, perchloric acid, ammoniumnitrate, silver nitrate, benzoyl peroxide, tetranitromethane, sodiumperchlorate, potassium perchlorate, potassium permanganate, potassiumpersulfate, sodium nitrate, potassium chromate, and a combinationthereof.
 14. A method according to claim 1, further comprising changinga color of the layer of the composite gel by applying an electricalsignal thereto.